@radji Ran into this while I was researching my own struggles outputting dual monitors from my Pi 4. I found a way to get it done - I'll spare you the walkthrough if that's okay but it involved booting the desktop environment first with xrandr installed and the displays configured there - then rigging the thing to autostart emulation station from there on top of that environment. Long story short, I took a huge performance hit, even the gen. 4 consoles started dropping frames and chopping audio. I was super proud to get it working after many failures and posts online saying it couldn't be done, but unfortunately it just wasn't worth it in the end. Most people suggest an HDMI splitter and now that I can see how rough it can be on the system to make this work - just don't do it is my advice. Maybe it's a moot point for you by now, but FYI for anyone else down the road. Go with the splitter.